| 年度 | 实际值 |
|---|---|
| 1995 | 33.7 |
| 1996 | 34.7 |
| 1997 | 35.29 |
| 1998 | 33.4 |
| 1999 | 33.9 |
| 2000 | 31.8 |
| 2001 | 30.43 |
| 2002 | 29.13 |
| 2003 | 27.18 |
| 2004 | 25.59 |
| 2005 | 23.07 |
| 2006 | 22.21 |
| 2007 | 21.37 |
| 2008 | 21.92 |
| 2009 | |
| 2010 | 20.27 |
| 2011 | 20.35 |
| 2012 | 21.33 |
| 2013 | 20.59 |
| 2014 | 19.72 |
| 2015 | 19.64 |
| 2016 | 19.8 |
| 2017 | |
| 2018 | 17.67 |